People who put in at least 55 hours per week at work were more likely to be diagnosed with Type 2 diabetes

Do you ever feel like your job is killing you? If you work long hours, your job might be giving you diabetes.

Health experts have noticed for years that people who spend a lot of time at work are more likely to have various types of health problems, including stress, cardiovascular disease and depression. But efforts to find a direct link between work hours and Type 2 diabetes have been mixed. For instance, a study of manual laborers in Japan found that those who worked more than 53 hours a week had a higher risk of diabetes, while Japanese office workers who logged more than 55 hours a week did not.

To get to the bottom of this, an international team of researchers scoured the medical literature and found reliable data on 222,120 adults from the United States, Europe, Australia and Japan. Many of them were hard workers -- depending on the study they were involved in, up to 68% of them worked “long hours” (generally defined as more than 55 hours per week).

A total of 4,963 of these men and women were diagnosed with Type 2 diabetes during the time they were tracked by researchers. But not everyone had the same risk of getting that diagnosis.

Compared with people who worked 35 to 40 hours per week, those who worked at least 55 hours per week were 7% more likely to develop the metabolic disorder, in which high blood sugar can lead to serious problems like stroke, kidney failure or blindness.

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When the researchers accounted for workers’ socioeconomic status, the results were more striking. For those with high incomes, there was no link between hours worked and diabetes risk. The results for people in the middle-income territory were weak but suggested a link between hours worked and diabetes risk.

However, for those with low incomes, working long hours was associated with a 29% increased risk of developing diabetes. After the researchers adjusted for other demographic factors, the risk dropped slightly, to 26%.

The researchers noted that the link held up for low-income workers regardless of which study they were in, how they were diagnosed (fasting glucose test, glucose tolerance test or self-reporting), or their age, gender or obesity status.

The results were published online Thursday by the journal Lancet Diabetes and Endocrinology.

The study couldn’t determine why longer hours would make some people more prone to Type 2 diabetes, but the researchers offered some possible explanations. For instance, people who spend more time at their jobs may have less time to exercise, take part in stress-reducing social activities or sleep. Other research has shown that sleep-deprivation and fragmented sleep can interfere with the body’s ability to make and use insulin, which leads to high blood sugar.

On the other hand, high-income workers who put in long hours have more resources to help them deal with the stresses caused by having less free time -- paying for child care, household help and prepared foods, to name a few examples. But if there were anything inherently dangerous about a long work week, then high-income workers should see their risk of diabetes increase too, at least a little.

In a commentary that accompanies the study, a pair of Harvard researchers wrote that it’s too early to rule out the idea that “working long hours per se is toxic.”

The influence of sleep is probably important, the Harvard researchers added. Perhaps people who work long hours in well-paid jobs have more predictable schedules than people who work in lower-paying jobs and wind up working overtime.

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